1. Field of the Invention
The invention generally relates to semiconductor devices and fabrication of the same.
2. Background Information
It is desirable to form smaller geometries or dimensions for semiconductor devices for a number or reasons including to decrease manufacturing costs. A smaller semiconductor device uses less area on a wafer so that additional devices can be formed in the same area of a wafer. More dense features allows for more dense devices, such as increased channel width in MOSFETs which leads to lower on resistance. Additionally, by providing finer geometry devices, die size can be reduced in order to reduce manufacturing costs of devices.
Semiconductor devices of various kinds are well known in the prior art. One semiconductor device that is well known is a semiconductor diode. Semiconductor diodes are widely used in electronic circuits for various purposes. The primary purpose of such semiconductor diodes is to provide conduction of current in a forward direction in response to a forward voltage bias, and to block conduction of current in the reverse direction in response to a reverse voltage bias. This rectifying function is widely used in such circuits as power supplies of various kinds as well as in many other electronic circuits.
In manufacturing semiconductor devices, the fabrication process typically includes etching and diffusion. Etching is a process where material is removed from a substrate, a layer or thin film that was placed on a substrate. Diffusion is a process where a dopant is introduced into a material and diffuses therein as a gradient of the dopant. In either case, a pattern is typically used to selectively etch or diffuse a dopant in areas of a semiconductor wafer for manufacturing semiconductor devices.
Etching can be accomplished by a wet etch process or a dry etch process. A wet etch process typically involves removing exposed material in a wet acid bath. A dry etch process avoids the use of a wet acid bath and typically uses a chemical introduced by a gas under pressure or into a chamber with lower than atmospheric pressure with ions excited by an excitation energy. An etch process which etches a material in all directions at the same rate is said to be isotropic. An etch process which has a horizontal etch rate that differs from a vertical etch rate for a material is not isotropic but is said to be anisotropic. A lateral etch ratio Lr is defined as the ratio of the etch rate in the horizontal direction to the etch rate in the vertical direction for a give material. Lr=(Horizontal Etch Rate of Material/Vertical Etch Rate of Material). The degree of anisotropy A=(1−Lr).
Diffusion can be accomplished by supplying a dopant to the semiconductor material and heating the dopant and the semiconductor material together to diffuse the dopant into the silicon. Supplying the dopant to the semiconductor material can be accomplished by implanting the dopant by ion implantation methods. To complete the diffusion step, the semiconductor material is heated with the implanted dopant to diffuse the dopant into the semiconductor material.
In order to form a pattern of diffusion or to etch a pattern of material, a mask or photoresist material is typically used to protect material that is not to be etched or is not to have a dopant diffused therein and expose material that is to be etched or is to have a dopant diffused therein. Other known methods can be used to protect material as well as expose material to form a pattern for etching and diffusing.